This invention relates to methods for making curable melt processed materials comprising mixtures of polyphenylene ether (PPE) and polystyrene (PS), particularly high impact polystyrene (HIPS), with uncured epoxy components which comprise a curable epoxy and an epoxy curing agent, curable materials made by this method, and materials resulting from the subsequent cure of those materials.
It is a common practice in the industry to blend a small amount of elastomeric or thermoplastic material into a hard thermosetting resin in order to toughen (i.e., increase the ductility of) the thermoset. Elastomeric or thermoplastic toughening agents include natural rubbers, polyolefins, and vinyl copolymers such as poly(styrene-co-butadiene). In such cases, the toughening agent is blended in a ratio of from about 1:20 to about 1:4 with a curable thermosetting resin such that the thermoplastic component becomes the dispersed phase in a thermosetting resin continuous phase.
U.S. Pat. No. 5,709,948 discloses curable mixtures of polyolefin resins and epoxies. Curable mixtures comprising PPEs are not disclosed.
EP 592,145 and U.S. Pat. No. 4,912,172 disclose curable compositions consisting essentially of a polyphenylene ether (PPE), an epoxy, a zinc or aluminum catalyst, and, in some cases, an imide co-catalyst. These references do not teach that a curable melt processed composition of greater than 50% thermoplastic can be obtained. These references disclose solvent mixing of the components or mixing wherein a liquid epoxy is the major component. These references do not teach the use of a PPE/HIPS blend thermoplastic. These references disclose materials for structural use rather than for use as adhesives or coatings.
U.S. Pat. No. 5,001,010 discloses a curable article comprising a mixture of an epoxy and an epoxy cure catalyst with a specific PPE obtained by melt processing the PPE at 230xc2x0 C.-290xc2x0 C. prior to addition of epoxy. This reference discloses solvent mixing of the epoxy with the melt-processed PPE and subsequent cure at 190xc2x0 C.-250xc2x0 C.
U.S. Pat. No. 5,308,565 discloses a prepreg board made with reinforcing fiber and a curable composition which preferably comprises PPE, a liquid epoxy, a flame retardant, and a curing catalyst, but at least comprising the first two elements. The blend is partially cured during mixing (""565 at col. 2, ln. 50) at 100-130xc2x0 C., so that it can be granulated and mixed with a substrate for final curing to form a mat. The reference emphasizes throughout that the mixing is performed at 100-130xc2x0 C. The reference recommends an epoxy content of greater than 50%. (""565 at col. 13, ln. 31). This reference discloses materials for structural use rather than for use as adhesives or coatings.
EP 137,545 discloses an article made from a blend of PPE, HIPS and an epoxy resin which is coated with a lacquer or adhesive. The material of the reference is required to receive a coating or adhesive and is not disclosed as being suitable for use as a coating or adhesive. The reference does not teach that the epoxy component is cured or uncured at any point. The reference does not teach curing the epoxy component or the inclusion of any curative or catalyst.
Venderbosch, Nelissen, Meijer and Lemstra, Makromol.Chem., Macromol. Symp. 75, pp. 73-84 (1993); Venderbosch, Meijer and Lemstra, POLYMER, Vol. 35, no. 20, pp. 4349-4357 (1994); and Venderbosch, Meijer and Lemstra, POLYMER, Vol. 36, no. 6, pp. 1167-1178 (1995) disclose melt mixing combinations of PPE and epoxy monomers. These references do not describe PPE/PS/epoxy mixtures nor the use of compatiblizers with such mixtures.
Briefly, the present invention provides a method of making a curable melt blended composition by melt blending 60 to 99.9 weight percent of a thermoplastic component, comprising 1-99 weight percent of polyphenylene ether (PPE) polymer, and 1-99 weight percent of polystyrene polymer, preferably high impact polystyrene (HIPS) polymer; and 0.1 to 40 weight percent of an uncured epoxy component, comprising a curable epoxy and an effective amount of a curing agent for said curable epoxy, where melt blending occurs at a temperature greater than 150xc2x0 C. and is achieved without addition of solvent and the epoxy component of the resulting composition is substantially uncured.
In another aspect, the present invention provides a curable melt blended composition comprising 60 to 99.9 weight percent of a thermoplastic component, comprising 1-99 weight percent of polyphenylene ether (PPE) polymer, and 1-99 weight percent of polystyrene polymer, preferably high impact polystyrene (HIPS) polymer; and 0.1 to 40 weight percent of an uncured epoxy component, comprising a curable epoxy and an effective amount of a curing agent for said curable epoxy, wherein the epoxy component of the resulting composition is substantially uncured.
In another aspect, the present invention provides a cured material resulting from the heat or light cure of the curable melt blended composition provided herein.
In another aspect, the present invention provides an adhesive or coating comprising the curable melt blended composition provided herein or the cured material resulting from the heat or light cure of the curable melt blended composition provided herein.
What has not been described in the art, and is provided by the present invention, is a curable melt processed composition of PPE/polystyrene, epoxy and an epoxy curative, and, optionally, a compatibilizer, wherein the thermoplastic is the major component. In particular, the art does not disclose or teach the method, or the resulting material, wherein PPE/PS, epoxy and epoxy curing agent and, optionally, a compatibilizer, are combined by melt processing, without solvent, at greater than 150xc2x0 C., to result in a curable composition wherein the epoxy component remains substantially uncured. Furthermore, the art does not disclose or anticipate the improved peel and overlap shear strengths exhibited by the PPE/PS/epoxy blends relative to PPE/epoxy blends.
In this application:
xe2x80x9ccuring agentxe2x80x9d, for epoxy, means an epoxy curative or an epoxy catalyst;
xe2x80x9cdoes not substantially heat curexe2x80x9d, used in regard to a composition containing an epoxy component, means remains substantially uncured,
xe2x80x9csubstantially uncuredxe2x80x9d means at least half of the reactive sites for polymerization in a population of monomeric units remain unreacted, preferably more than about 90% remain unreacted and most preferably more than about 95% remain unreacted, and
xe2x80x9csubstitutedxe2x80x9d means substituted by conventional substituents which do not interfere with the desired product, e.g., substituents can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I), cyano, nitro, etc.
It is an advantage of the present invention to provide a method for making materials which exhibit improved peel strength, shear strength and modulus at high temperatures. It is a further advantage to provide such a material in a curable state, which may be applied as an adhesive or coating before cure. It is a further advantage to provide such material which is suitable for uses as an adhesive in electronics applications.